We are currently engaged in study of several aspects of site specific cleavage and methylation of DNA. The E. coli RI DNA restriction and modification enzymes, are being analyzed as a model system for study of sequence-specific DNA protein interaction. The interaction of the Eco RI enzymes with short DNA molecules will be investigated with the aim of obtaining thermodynamic and kinetic parameters governing the interaction. Utilizing absorbance and fluourescence methods, we hope to apply rapid kinetic methods to analysis of such interactions. We have cloned the structural genes for the Eco RI enzymes, and are sequencing the corresponding DNA fragment in order to obtain the primary sequences of the two proteins. In a related vein, we have undertaken study of the "ter" system of virus P2, the enzyme system responsible for site specific cleavage of viral DNA prior to packaging into the virion. Three components necessary for this reaction have been obtained in pure form, and "ter" cleavage has been demonstrated in vitro. The mechanism of this reaction is under investigation, with emphasis on identification of intermediates in the process.